1. Field of the Invention
The present invention relates to an optical functional device of a waveguide type, in particular the one which has an organic nonlinear optical material as an element and is suitable for use in the field of optical communication or optical information treatment.
2. Description of the Prior Art
It has recently been recognized from experimental and theoretical researches that organic compounds having nonlocalized .pi. electrons exhibit an extremely large nonlinear optical response. In particular, for second order nonlinear optical constants, many compounds have been found at the molecular level which have a nonlinear optical constant of two figure larger than those of known inorganic crystals such as LiNbO.sub.3 or the like, and researches have been successively conducted looking into the crystallization of these compounds.
These organic nonlinear optical crystals are considered very hopeful as new materials in the application fields such as optical modulation, optical frequency modulation, optical bistability, phase conjugate optics or the like, and thus many methods for incorporating the crystals into a device have hitherto been proposed. There has recently been examined also a unit mode waveguide as well as conventional multimode waveguides as the optical functional device of a waveguide type. However, all of these proposals are only for the formation of multimode waveguides as described in Optical Communications, 50, 154 (1984) or ACS Symposium series 233, 153 (1983), in which a channel having a width of about 100 .mu.m is provided on a substrate and filled with a molten nonlinear optical material, or the molten material are charged into a hollow optical fiber having an internal diameter of 2-10 .mu.m by capillarity.
On the other hand, optical functional devices of a waveguide type are in many cases constituted of a unit mode waveguide having a narrow core width and electrodes for controlling waveguided light by an electro-optic effect, acoustooptic effect or the like.
However, amongst the aforementioned conventional techniques regarding the formation of a unit mode waveguide, the former method in which a channel is provided and filled with a molten nonlinear optical material has a problem in that it is very difficult to fill the channel having a prescribed depth and width with the molten material because of the channel having a narrow diameter of several micrometers.
The latter method among the aforementioned conventional techniques in which a molten nonlinear optical material is charged into a hollow optical fiber also has a problem in that it is difficult to make a unitary construction with the electrodes or with other optical parts, that is, it is difficult to effect an optical integration.